Libya's ex-leader Col Muammar Gaddafi has been killed after an assault on his birthplace of Sirte, officials say.

The circumstances of his death are not yet clear. Video has emerged purporting to show Col Gaddafi being captured alive and bundled on to a truck.

Fighters loyal to the National Transitional Council (NTC) said they found him hiding in a hole, and shot him when he tried to escape.

Col Gaddafi was toppled in August after 42 years in power.

US President Barack Obama said this was a "momentous day" for Libya, now that tyranny had fallen. He said Libya had a "long and winding road towards full democracy", but the US and other countries would stand behind it.

The colonel was fighting in Sirte alongside his two sons, Mutassim and Saif al-Islam, according to reports.

Officials say Mutassim was killed in battle on Thursday.

The NTC's justice minister Mohammad al-Alagi told the AP news agency Saif al-Islam had been captured and taken to hospital with a leg wound.

Golden gun

After a day of conflicting reports and rumours, the NTC's acting prime minister Mahmoud Jibril told a news conference: "We have been waiting for this moment for a long time. Muammar Gaddafi has been killed."

World leaders welcomed the news, urging the NTC to carry through its promise to reform the country.

UK Prime Minister David Cameron, who had taken a leading role in Nato's intervention, said it was "a day to remember all of Col Gaddafi's victims".

UN Secretary General Ban Ki-moon called it a "historic" moment, but warned: "The road ahead for Libya and its people will be difficult and full of challenges."

Proof of Col Gaddafi's fate came in grainy pieces of video, first circulated among NTC fighters and then broadcast by international news channels.

The first videos showed a bloodied corpse, with some channels picking up footage they said showed the colonel's body being dragged through the streets.

An NTC fighter told the BBC he found Col Gaddafi hiding in a hole in Sirte, and the former leader begged him not to shoot.

The fighter showed reporters a golden pistol he said he had taken from Col Gaddafi.

Arabic TV channels showed images of troops surrounding two large drainage pipes where the reporters said Col Gaddafi was found.

Later, another video emerged of the colonel being bundled on to the back of a pick-up truck after being captured alive.

NTC fighters said he was shot when he tried to escape.

None of the video footage has been independently verified.

'United Libya'

Libyans gathered in towns and cities across the country to celebrate the reports of the colonel's death.

Groups of young men fired guns in the air, and drivers honked horns in celebration.

His death came after weeks of fierce fighting for Sirte, one of the last remaining pockets of resistance.

Nato, which has been running a bombing campaign in Libya for months, said it had carried out an air strike earlier on Thursday that hit two pro-Gaddafi vehicles near Sirte.

It was unclear whether the strikes were connected with Col Gaddafi's death.

Mr Jibril promised that National Transitional Council (NTC) chief Mustafa Abdul Jalil would give more details of how Col Gaddafi was killed either late on Thursday or during Friday.

He said Mr Abdul Jalil would also officially announce the "liberation of the country", allowing the NTC to begin pushing through democratic reforms that will lead to elections.

"I think it's for the Libyans to realise that it's time to start a new Libya, a united Libya, one people, one future," Mr Jibril said.

I have been waiting for 247 days to hear this news. When the protests started on February 15th, I immediately tuned in to AlJazeera and CNN for the latest news, and I have tuned in every day since. Gadhafi used warplanes, ships, and a multitude of soldiers against his own people. Now, they have turned against him, and won. This civil war is over.

I have been waiting for 247 days to hear this news. When the protests started on February 15th, I immediately tuned in to AlJazeera and CNN for the latest news, and I have tuned in every day since. Gadhafi used warplanes, ships, and a multitude of soldiers against his own people. Now, they have turned against him, and won. This civil war is over.

A soldier who says he captured Muammar Gaddafi tod the BBC the colonel had shouted: "Don't shoot!"

I am not going to leave this land. I will die as a martyr at the end. I shall remain, defiant. Muammar is Leader of the Revolution until the end of time.
- Televised address to the nation, quoted in guardian.co.uk (22 February 2011) "Gaddafi urges violent showdown and tells Libya 'I'll die a martyr'" by Ian Black